Glazing materials sometimes include one or more functional layers engineered to enhance the performance of the glazing. One important functional layer reduces transmission of infrared radiation. Infrared-rejecting functional layers are typically made of partially transparent metallized or dyed polymer film constructions that reflect or absorb unwanted solar radiation. References describing such functional layers include U.S. Pat. Nos. 4,590,118, 4,639,069 and 4,799,745.
An especially useful infrared-rejecting functional layer can be formed from an infrared-rejecting Fabry-Perot quarter wave stack. In such a stack, a transparent dielectric spacing layer separates two or more partially reflective thin metal or metal alloy layers. The metal or metal alloy layers (which for brevity will sometimes be referred to herein as “metal layers”) typically contain elemental or alloyed silver, copper or gold. The dielectric layer typically contains an inorganic oxide (applied from an organic solution or applied using sputter deposition) or an organic polymer (applied by dissolving the polymer in a solvent solution). The dielectric layer optical thickness (defined as the physical thickness of the dielectric layer times its in-plane index of refraction) preferably is about ¼ the wavelength of the center of the desired pass band. Light whose wavelength is within the pass band is mainly transmitted through the thin metal layers. Light whose wavelength is above the pass band is mainly reflected by the thin metal layers or suppressed due to destructive interference. References describing such infrared-rejecting Fabry-Perot quarter wave stacks include U.S. Pat. Nos. 4,590,118, 4,639,069 and 4,799,745.
Infrared-rejecting functional layers have also been made from birefringent non-metallic films containing alternating layers of dielectric materials. Birefringent dielectric multilayer films (which can also be referred to as a multilayer optical films or “MOF”) can be engineered to reflect or absorb a desired amount of light in a spectral region of interest while transmitting sufficient visible light in the visible region of the spectrum to be substantially transparent. Multilayer optical films preferably include alternating layers of a first material having a first index of refraction and a second material having a second index of refraction that is different from the first index of refraction. Multilayer optical films can have a Brewster angle (the angle at which reflectance of p polarized light goes to zero) that is very large or nonexistent. The films can be made into a multilayer mirror whose reflectivity for p polarized light decreases slowly with angle of incidence, is independent of angle of incidence, or increases with angle of incidence away from the normal. Multilayer optical films can have high reflectivity (for both s and p polarized light) for any incident direction. References describing such multilayer optical films include U.S. Pat. Nos. 5,699,188, 5,882,774 and 6,049,419, and PCT Published Application No. 97/01778.